...and now I can upload a screen image...

Please post your Troubleshooting Information. At the top right of the Thunderbird window, click the menu button , then select Help > Troubleshooting Information. Press the "Copy text to clipboard button" and paste the information into your reply.

Application Basics

   Name: Thunderbird
   Version: 52.9.1
   User Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1
   Profile Folder: Open Folder

             (Local drive)
   Application Build ID: 20180709124824
   Enabled Plugins: about:plugins
   Build Configuration: about:buildconfig
   Memory Use: about:memory
   Profiles: about:profiles

 Mail and News Accounts
   account1:
     INCOMING: account1, , (imap) mail.ishoo.co.uk:143, alwaysSTARTTLS, passwordCleartext
     OUTGOING: , smtp.ishoo.co.uk:587, plain, passwordCleartext, true

   account2:
     INCOMING: account2, , (none) Local Folders, plain, passwordCleartext

   account3:
     INCOMING: account3, , (imap) imap.mail.me.com:993, SSL, passwordCleartext
     OUTGOING: , smtp.mail.me.com:587, alwaysSTARTTLS, passwordCleartext, true

 Crash Reports

 Extensions
   Lightning, 5.4.9.1, true, {e2fda1a4-762b-4020-b5ad-a41df1933103}

 Important Modified Preferences

   Name: Value

     accessibility.lastLoadDate: 1524124668
     browser.cache.disk.capacity: 358400
     browser.cache.disk.filesystem_reported: 1
     browser.zoom.full: true
     extensions.lastAppVersion: 52.9.1
     font.internaluseonly.changed: false
     font.name.monospace.el: Consolas
     font.name.monospace.x-cyrillic: Consolas
     font.name.monospace.x-unicode: Consolas
     font.name.monospace.x-western: Consolas
     font.name.sans-serif.el: Calibri
     font.name.sans-serif.x-cyrillic: Calibri
     font.name.sans-serif.x-unicode: Calibri
     font.name.sans-serif.x-western: Calibri
     font.name.serif.el: Cambria
     font.name.serif.x-cyrillic: Cambria
     font.name.serif.x-unicode: Cambria
     font.name.serif.x-western: Cambria
     font.size.fixed.el: 14
     font.size.fixed.x-cyrillic: 14
     font.size.fixed.x-unicode: 14
     font.size.fixed.x-western: 14
     font.size.variable.el: 17
     font.size.variable.x-cyrillic: 17
     font.size.variable.x-unicode: 17
     mail.openMessageBehavior.version: 1
     mail.winsearch.firstRunDone: true
     mailnews.database.global.datastore.id: 0b2d359e-ee92-42f4-85f2-9ec01db27e7
     mailnews.database.global.views.conversation.columns: {"threadCol":{"visible":true,"ordinal":"1"},"flaggedCol":{"visible":true,"ordinal":"3"},"attachmentCol":{"visible":false…
     media.gmp.storage.version.observed: 1
     network.cookie.prefsMigrated: true
     network.predictor.cleaned-up: true
     places.database.lastMaintenance: 1539344286
     places.history.expiration.transient_current_max_pages: 48999
     print.printer_EPSON3D5F1E_(WF-7620_Series)_Land.print_bgcolor: false
     print.printer_EPSON3D5F1E_(WF-7620_Series)_Land.print_bgimages: false
     print.printer_EPSON3D5F1E_(WF-7620_Series)_Land.print_duplex: -437918235
     print.printer_EPSON3D5F1E_(WF-7620_Series)_Land.print_edge_bottom: 0
     print.printer_EPSON3D5F1E_(WF-7620_Series)_Land.print_edge_left: 0
     print.printer_EPSON3D5F1E_(WF-7620_Series)_Land.print_edge_right: 0
     print.printer_EPSON3D5F1E_(WF-7620_Series)_Land.print_edge_top: 0
     print.printer_EPSON3D5F1E_(WF-7620_Series)_Land.print_evenpages: true
     print.printer_EPSON3D5F1E_(WF-7620_Series)_Land.print_footercenter:
     print.printer_EPSON3D5F1E_(WF-7620_Series)_Land.print_footerleft: &PT
     print.printer_EPSON3D5F1E_(WF-7620_Series)_Land.print_footerright: &D
     print.printer_EPSON3D5F1E_(WF-7620_Series)_Land.print_headercenter:
     print.printer_EPSON3D5F1E_(WF-7620_Series)_Land.print_headerleft: &T
     print.printer_EPSON3D5F1E_(WF-7620_Series)_Land.print_headerright: &U
     print.printer_EPSON3D5F1E_(WF-7620_Series)_Land.print_in_color: true
     print.printer_EPSON3D5F1E_(WF-7620_Series)_Land.print_margin_bottom: 0.5
     print.printer_EPSON3D5F1E_(WF-7620_Series)_Land.print_margin_left: 0.5
     print.printer_EPSON3D5F1E_(WF-7620_Series)_Land.print_margin_right: 0.5
     print.printer_EPSON3D5F1E_(WF-7620_Series)_Land.print_margin_top: 0.5
     print.printer_EPSON3D5F1E_(WF-7620_Series)_Land.print_oddpages: true
     print.printer_EPSON3D5F1E_(WF-7620_Series)_Land.print_orientation: 0
     print.printer_EPSON3D5F1E_(WF-7620_Series)_Land.print_page_delay: 50
     print.printer_EPSON3D5F1E_(WF-7620_Series)_Land.print_paper_data: 9
     print.printer_EPSON3D5F1E_(WF-7620_Series)_Land.print_paper_height: 297.00
     print.printer_EPSON3D5F1E_(WF-7620_Series)_Land.print_paper_name:
     print.printer_EPSON3D5F1E_(WF-7620_Series)_Land.print_paper_size_unit: 1
     print.printer_EPSON3D5F1E_(WF-7620_Series)_Land.print_paper_width: 210.00
     print.printer_EPSON3D5F1E_(WF-7620_Series)_Land.print_resolution: 600
     print.printer_EPSON3D5F1E_(WF-7620_Series)_Land.print_reversed: false
     print.printer_EPSON3D5F1E_(WF-7620_Series)_Land.print_scaling: 1.00
     print.printer_EPSON3D5F1E_(WF-7620_Series)_Land.print_shrink_to_fit: true
     print.printer_EPSON3D5F1E_(WF-7620_Series)_Land.print_to_file: false
     print.printer_EPSON3D5F1E_(WF-7620_Series)_Land.print_unwriteable_margin_bottom: 0
     print.printer_EPSON3D5F1E_(WF-7620_Series)_Land.print_unwriteable_margin_left: 0
     print.printer_EPSON3D5F1E_(WF-7620_Series)_Land.print_unwriteable_margin_right: 0
     print.printer_EPSON3D5F1E_(WF-7620_Series)_Land.print_unwriteable_margin_top: 0
     security.sandbox.content.tempDirSuffix: {b3c9f710-6abc-4b1d-b886-28ebc94a0aea}

 Graphics

     GPU #1
     Description: Intel(R) HD Graphics 6000
     Vendor ID: 0x8086
     Device ID: 0x1626
     RAM: Unknown
     Drivers: igdumdim64 igd10iumd64 igd10iumd64 igd12umd64 igdumdim32 igd10iumd32 igd10iumd32 igd12umd32
     Driver Version: 20.19.15.4835
     Driver Date: 10-16-2017

     Features
     Direct2D: false
     DirectWrite: true (10.0.17134.1)
     WebGL Renderer: Google Inc. -- ANGLE (Intel(R) HD Graphics 6000 Direct3D9Ex vs_3_0 ps_3_0) -- OpenGL ES 2.0 (ANGLE 2.1.0.2a250c8a0e15)

     AzureCanvasBackend: skia
     AzureCanvasAccelerated: 0
     AzureFallbackCanvasBackend: cairo
     AzureContentBackend: skia

 JavaScript

 Incremental GC: 1

 Accessibility

   Activated: 0
   Prevent Accessibility: 0

 Library Versions

     Expected minimum version
     Version in use

     NSPR
     4.13.1
     4.13.1

     NSS
     3.28.6
     3.28.6

     NSS Util
     3.28.6
     3.28.6

     NSS SSL
     3.28.6
     3.28.6

     NSS S/MIME
     3.28.6
     3.28.6

INCOMING: account1, , (imap) mail.ishoo.co.uk:143, alwaysSTARTTLS, passwordCleartext

There's a mismatch in your server configuration. Make sure you do use the configuration as per your email providers instructions. Check with your email provider about the correct server settings and post them here.

Thanks. I'll check my email providers instructions.

Two thoughts though...

As I haven't changed my account settings in Thunderbird for months, why would there be a mismatch starting today?

What are the items that don't match?

Port 143 doesn't match with STARTTLS.

You might want to have a look at the certificate using the view button and check who issued it and when it is due to expire.

I do know that Symantec exited the SSL/TLS certificate market and that certificates issues by them, as Symantec, Thawte, GeoTrust, and RapidSSL were set to be distrusted from about now, so perhaps your server has a no longer accepted issuing authority.

A test of the server See here indicated that Thawte is in the root of the certificates, so that angle is well worth considering. Although the test did highlight a number of other security weaknesses in the server configuration. Not the least of which is the certificate identifies itself as being for mail.livemail.co.uk .

If you are satisfied to use a certificate for mail.livemail.co.uk for the encryption for your communications, that is up to you and why there is an add permanent exception button in the dialog.

Thanks for your help.

Unfortunately, I know nothing about security certificates so making a sensible response is going to be difficult.

However, I see the name "thawte" in the window that opens when clicking "View". See attached.

I don't know anything about mail.livemail.co.uk. Is it a bad thing?

Is this a problem I should raise with Fasthosts, my email provider?

I'll check my email providers instructions.

Did you do that? Please post your email providers server settings here. Presumably they do have a support web site. This has got nothing to do with certificates.

I changed the server name to an alternative one that my provider suggested and the error messages have gone.

Thanks for your help.

It "feels" like I am being "attacked" and I don't have a clue where it's coming from and what to do to correct it!

captaindrew,

please start a new topic for your problem. https://support.mozilla.org/questions/new

NO idea WHAT you are talking about!!! I NEED help . . my Thunderbird is TITS UP!! Someone is "hacking" me!!

captaindrew said

NO idea WHAT you are talking about!!! I NEED help . . my Thunderbird is TITS UP!! Someone is "hacking" me!!

Then use the link your were provided with a ask a new question. I will be locking this thread as it is "solved" to the satisfaction of it's owner. The information here does not obviously meet your needs so this topic is officially closed. I would point out that certificate issues are generally caused by Anti virus programs hack you, not real hackers.

In this case it is probably down to using a cheap hosting plan without appropriate certificates and then using connection encryption. In this instance from Rackspace.